Eye tracking (also called gaze tracking) technology is evolving to become an important part of next generation human-computer interfaces. Eye tracking technology has many potential applications in entertainment, research, and as an interaction tool for people who are physically impaired.
Most known video-based eye tracking systems use infrared (IR) cameras with IR light sources to detect the pupil/iris as well as glints from the illumination. Additionally, these systems generally use either direct imaging or indirect imaging. Direct imaging systems image the eye region directly by placing one or more IR sensors directly aimed at the eyes. These systems have problems, however, with occlusion of the sensor (e.g., from eyelashes) as well as the user's vision (e.g., from the sensor). These systems have particular trouble tracking the eyes of people who wear eyeglasses, at least partly because the eyeglasses cause occlusions or disturb the computer vision algorithms by creating false specular reflections.
Indirect imaging systems partly address the occlusion problem by viewing the eye via a so-called “hot mirror” lens, which acts as a mirror to near-IR limitation but as pass-through glass to visible light. In that way, the sensor can view the eye from a frontal position while avoiding occlusion of the user's field of view. However, the indirect imaging approach requires special glasses (i.e., equipped with hot mirror lenses) and, therefore, is not suitable for people who depend on standard (prescription) eyeglasses.